Lipo charging setup for the bed of my truck

[burleyman]

Dave in AZ, using the 7 pin may seem a little crude.

It's all about charging voltage. I have two vehicles for camping. My Silverado with smart charging will maintain about 14.5vdc as long as the park or headlights are on. My van's dumb alternator's voltage varies between 14.1 and 14.7vdc. These are within most batteries recommended charging voltage. If you don't have it, slow and incomplete charging. How much drive time?

Wiring distance from front to back can produce a voltage loss and a lower voltage applied to the rear battery. That results in lower charging amps.

Testing can also be a little crude. Locate the fuse for the 7 pin connector lead at the front, and have replacements. After draining the rear battery, connect it. If the fuse doesn't blow, good. Monitoring charging amps and voltage is a plus.

Lead acid charging amps will start out high and quickly diminish.

A lifepo4 with low internal resistance, amps will remain fairly constant until charged.

Charging a 100ah lifepo4 from the 7 pin might not be possible. I'm ignorant. Ive only tested 100ah lead acid and 30ah lithium.

DC to DC takes care of all that, but can limit charging amps to below what the alternator could easily provide and what the battery can accept. Slower charging.

It also takes care of forgetting to unplug the 7 pin connector. I've done that twice in the last seven years.

 

[SlowCarFast]

Cool, I think I'll move the wire size up to #6 to CMA . I found some marine grade breakers that should work at the boat store. They can surface mount.
To your point about mounting the breakers close to the power source, that would mean between the charging battery and the DC charger the first one would want to be closest to the charging battery. Then for the protection in between the charger and the house battery, would the protection want to be closer to the charger, or the house battery?

Also, I've heard this charger (renogy) may not work right if I just run the negative to the chassis. I should plan on two runs all the way back to the starter battery correct?
I think it needs a control wire from the ignition, which I didn't plan for originally.

Yes, 1 fuse close to the charging/starter battery. Between the DC charger and house battery I think I actually double fused mine (one on each end). That might be overkill, but the thought was, if my hot wire were to be inadvertently grounded in between, then while charging, you'd want a fuse close to the charger, while not charging, you'd want a fuse close to the battery. the fuse assemblies were relatively cheap from wherever I got them so it seemed like good enough insurance. Mine is also a bit more complicated with distribution bus bars and a smaller accessory fuse box because I'm powering a fridge plus a handful of outlets for other stuff, but the principle is the same.

I have one of the Renogy solar/DC to DC chargers and my ground is to a chassis ground point in the rear. So only one wire from the engine bay. I hadn't heard that about ground issues with those units and I didn't have any issues. The control wire is apparently only for "smart alternators" (more info here: https://www.redarcelectronics.com/u...ators-faqs/smart-alternator-fixed-alternator/) which have variable voltage outputs. I think for standard voltage output alternators it's unnecessary. I didn't use it and it's worked fine in my case (2014 model).